The invention relates to filler necks for the fuel tank of a motor vehicle, having a funnel-type insert and, adjoining the latter in the inward direction, a pivotable flap with a locking element which can be pivoted counter to the force of a spring by the filler tube of a gas-pump nozzle so as to release the flap. For refueling purposes, the filler tube of a gas-pump nozzle is inserted into the funnel part, the diameter of the filler tube differing in dependence on the type of fuel. The diameter is large enough for diesel and leaded gasoline (the use of which is dying out) and small for unleaded gasoline. The narrowest diameter of the funnel part is selected correspondingly.
It is not possible to insert the relatively thick filler tube into the narrower funnel. How is it possible, however, to prevent the relatively thin end tube from being inserted into the wider funnel? This is the question on which the invention is based.
Ep 11 99 208 A1 discloses a solution to this problem. This consists in the inner part of the funnel being somewhat narrower than the relatively wide end tube used for diesel fuel and being displaceable along its longitudinal axis. When the relatively wide end tube is inserted, it is displaced and releases the connection to a refueling venting line; it acts, to a certain extent, as a valve. This does not take place with the narrower end tube; the refueling venting means is blocked. It is not possible here, however, to prevent filling with the incorrect fuel. With a sufficiently small level of throughflow, that is to say if flow does not take place through the entire cross section of the filler tube.
In the case of a further device which is known from DE 100 51 212 A1, a flap known as an unleaded flap is secured by means of at least one locking lever which projects, by way of a shoulder, into the interior of a funnel-type insert. When a filler tube of sufficiently large diameter is inserted, the locking lever is forced to one side and the flap is opened. This does not take place if the diameter of the filler tube is too small. However, it has been found that the mechanism can be activated improperly if an excessively thin filler tube is inserted obliquely and moved about appropriately.
The invention, then, is to propose a solution which reliably prevents filling with the incorrect fuel; this is obviously to be done with the lowest possible level of structural outlay.